The present invention relates to a process for producing isoprene trimers through the use of catalysts having improved activity with improved selectivity to cyclic trimers.
Heretofore, for preparing oligomers of an 1,3-diolefin, a process for polymerizing 1,3-diolefins in the presence of a catalyst prepared by mixing an acetylacetonato compound of iron, cobalt or nickel with an organometallic compound of a metal selected from Groups I, II and III of the periodic table in the presence of an electron donor (e.g., Japanese Pat. No. 16882/63) has been known. Also known is a process for polymerizing an 1,3-diolefin in the presence of catalyst systems comprising a nickel complex such as nickel acetylacetonate, a reducing agent such as lithium boron hydride and a limited phosphite such as triphenyl phosphite (Zakharkin. Izuest. Akad, Nauk. S.S.S.R. 1964, 168). Furthermore, U.S. Pat. No. 2,972,640 discloses a process for producing dimethyl cyclooctadiene, which is a cyclic dimer of isoprene, as a main product by using a catalyst consisting of a complex of nickel carbonyl and triphenyl phosphite.
Recently, a process for producing a cyclic trimer of isoprene in which a catalyst comprising a combination of bisoctadiene nickel, a reducing agent and a particular phosphite in used (Japanese Pat. Nos. 56950/74 and 56951/74) has been proposed.
However, according to our belief, the prior methods referred to above may be further improved in the conversion of isoprene, concentration of catalyst used, or the selectivity to trimers.